my mpg has dropped down to 17mpg need help!!!

[ihpassat]

Hi guys, 2days ago the passat went for it's MOT and it failed on the front suspension arms! so got that fixed, and also the my startor motor, cause it was making a squeeling noise when i started the car up.
but anyways past few months i was getting around 24mpg driving in normal roads then today i notice i was only getting 17mpg!!!!!! anyone know what the common problem and is there anything i could test??

would of took it down to my mate who has a vag com, but he left to go to canada and wont be back till may!!!